Spinal fusion surgery is a method of placing bone graft material between two mobile segments of the spine to knit them together as one unit and eliminate motion between the segments. Fusion surgery can be performed with or without the use of spinal instrumentation for internal fixation. Internal fixation instruments are used to provide stability to decrease motion between segments of the spine and to allow the bone fusion to knit together. They act as an internal splint. Internal fixation devices may be attached with hooks, wires or bone screws. When bone screws orpedicle screws are employed they are screwed into the pedicles of a vertebra and connected to rods or plates to stabilize movement between the vertebrae to which they are connected. Thus, pedicle screws are implants used in the thoracic and lumbar spine to help surgeons stabilize the spine. “Headless” pedicle screws are used for several reasons, including the fact that headless screw design has been known to make it easier for surgeons to implant pedicle screws while avoiding the facet joint. In addition, pedicle screws can be implanted at each spinal level.
One such headless pedicle screw is the screw associated with TSRH-3D™ manufactured by Medtronic Sofamor Danek. More particularly, the present invention is capable of working in conjunction with “bolt 88” disclosed in U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson. The present invention is a replacement for the clamp found in U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson, the disclosures of which are specifically incorporated into this specification by reference. Details of the TSRH spinal implant system are disclosed in the “Surgical Technique Manual” provided by Danek Medical, Inc., published in 1990, which disclosure is also incorporated herein by reference.
The use of fixation devices for the treatment of vertebrae deformities and injuries is well known in the art. Various fixation devices are used in medical treatment to correct curvatures and deformities, treat trauma and remedy various abnormal spinal conditions. Treatment of these conditions generally requires the implantation of various component pieces such as support rods, crosslinks, caudal facing hooks, cranial facing hooks and like components, which form a spinal implant system.
It is necessary in spinal implant systems to properly anchor the system to bone to provide necessary support of the implant. Bone screws are commonly used for anchoring spinal implant systems. There are, however, several problems with the use of fixed screws for anchoring spinal implants. The exact final position of a bone screw is difficult, if not impossible, to predict prior to the exposure of the patient's bone. This unpredictability results from the uncertainty of exact bone formation and shape within an individual patient. Additionally, it can be difficult to predetermine the structure of the bone, i.e. whether the bone is soft or even osteoporotic. Even if the final position of the screw can be predetermined, the necessary shape and position of a spinal rod implant may create unwanted stress upon the bone screw or the bone itself. This is especially true where a plurality of screws is required along the spinal column for securement of an implant. The alignment of the rod with several screws along the vertebrae compounds this problem and makes undesired stress much more probable. Moreover, this misalignment may influence the extent and speed of correction of the spinal defect.
With regard to the size of a bone screw and connector, a low profile arrangement provides less disruption of the tissues in the vicinity of the spine. Nonetheless, it is common in the insertion of spinal implants to necessarily remove portions of vertebral bone to allow proper insertion of a bone screw. Moreover, current systems in use may result in long-term muscular displacement that may lead to a patient's pain or discomfort. Thus, a low profile bone screw and connector offers advantages, including less post-operative pain and discomfort for the patient.
Increased complexity of the installation procedure is undesirable because it increases a patient's time in surgery. Increased operating time is known to increase the risk of many complications associated with surgery. The additional time necessary to remove, or even temporarily dislocate, bone or muscular tissue also increases operating time, and thus the risk of complications.
In view of the above, there is a long felt but unsolved need for a method and system that avoids the above-mentioned deficiencies of the prior art and that provides an effective system that is relatively simple to employ and requires minimal displacement or removal of bodily tissue.